A vital materialist like Diderot had no problem with instrumental music since he had no real soul to worry about in any metaphysical sense; he could revel in the pure, secular sensation of its vibrations as the sounds oscillate violently through every nerve fibre of the body. Its power to excite was purely biological; it was not fixed by the authority of the rational soul, but depended on the particular disposition of a person's nervous system. In fact, Diderot speculates that there is no real difference between vocal and instrumental music, since a deaf-mute who suddenly awakens to sound would think that ‘music was a special way of communicating thoughts, and that the instruments … in our hands [are] other organs of speech’. These sounds would tingle over his senses, like little bells tinkling inside his body, and impress a tacit knowledge of harmony within him for his ‘soul’ (as a reflective rather than metaphysical entity) to attend to.

In such moments of pure secularisation, the knowledge of life could be an aesthetic act, a biological function of such intensity that one could almost ‘die of pleasure’. In effect, the divine mediation necessary in Cartesian epistemology between knowledge and reality is replaced by the immediacy of an aesthetic experience where sense and cognition could intermingle directly. If the flesh could live without spirit, then life could aspire to the condition of music's isomorphic relation with the body. In fact, for Diderot, the body could become a living instrument.